In networks connecting plural PCs for FA (Factory Automation), the following two functions ordinarily are found together.
(1) Cyclic Transmitting Function
A cyclic transmitting function is executed in which the delivery of ON/OFF signals among units connected to each other on a network, or the delivery of numeral data or the like, are executed by serial communications that do not pass through an I/O unit. The data occurring in each station on the network is altered or modified periodically and in real time.
(2) Transient Transmitting Function
A transient transmitting function is one in which a communicating station is only temporarily fixed between two stations, including a transmitting start-up initial station and a mating station, without having an effect or influence on the other stations, to execute transmitting of data.
Conventionally, the network between the PCs is arranged such that a link parameter (hereinafter referred to as "L-parameter") for controlling the network is prepared by a loader. The L-parameter is registered in a parent station, and is used to control and operate the network between the PCs. The contents of the L-parameter includes data identifying only the kinds or types of a data memory (hereinafter referred to as "link device") used by each of secondary or child stations on the network, and data for setting the capacity of the link device.
In each of the child stations, a setting (hereinafter referred to as "latching setting") can be made to control the latching/unlatching of the device into the network by a sequence parameter (hereinafter referred to as "S-parameter") for controlling operation of the PCs. By executing the latching setting at each child station, it is possible to protect the data of the device from a system-failure. The S-parameter is prepared by the loader similarly to the L-parameter, and is set for every child station. The L-parameter is contained or included in the S-parameter of the parent station.
FIG. 13 of the attached drawings is a block diagram showing an arrangement of a conventional network between the PCs. In FIG. 13, the reference numerals 1 and 2 denote stations connected to the network. Specifically, the reference numeral 1 denotes a parent station having an L-parameter for controlling the network, while the reference numeral 2 denotes each of a plurality of child stations which operate in accordance with the L-parameter. Further, the reference numeral 3 denotes each of a plurality of cables through which each station is connected to other stations. Normally, an optical fiber cable or a coaxial cable is used as each of the cables 3. The reference numeral 5 denotes a plurality of loaders for executing reading/writing of internal data within the PCs; 4 denotes a plurality of cables through which the loaders 5 are connected to the stations 1 and 2. In FIG. 13, the loaders 5 are connected to the stations 1 and 2.
FIG. 14 is a block diagram showing the arrangement within the conventional PCs (parent station 1 and child stations 2). In FIG. 14, the reference numeral 6 denotes a pair-loader transmitting and receiving control section for controlling communication of data between the loader 5 and the PCs (parent station 1 and child stations 2); 7, a data link control section for executing and controlling the cyclic transmitting function and the transient transmitting function; 8, a parameter setting data area for storing therein the S-parameter used for operating the stations and received from the loader 5; 9, a latching setting data area for storing therein the latching setting data in the S-parameter; and 10, a link setting data area for storing therein the L-parameter.
Further, the reference numeral 11 denotes a sequence program area for storing therein a sequence program received from the loader 5; 12, a sequence control section for controlling execution of the sequence program; 13, a 2-port RAM functioning as an interface (hereinafter referred to as "I/F") for communicating the data between the sequence control section 12 and the data link control section 7; and 14.about.19, data buses for executing transmission of the data.
FIG. 15 is a view showing an arrangement of a transmitting packet (frame) used during cyclic transmission. In FIG. 15, the reference numeral 74 denotes a packet to be transmitted; 75, a starting flag (SF) indicating the top or head of the packet 74; 76, a mating destination address (DA) to which the packet 74 is transmitted; 77, a control field (CTLF) including or containing information such as commands, a priority level and the like of the packet 74; 78, an address (SA) of a transmitting origin for transmitting the packet 74; 79, data (DATA) of the packet 74; 80, a frame check sequence (FCS) for detecting erroneous transmission by the packet 74; and 81, an end flag (EF) for indicating an end of the packet 74.
Here, it is assumed that an operator determines or decides a sequence program capacity, memory distribution or allocation for efficient use of the PCs, and other requisite arrangements or agreement facts, and also prepares the S-parameter and the sequence program using the loader 5 as illustrated in FIG. 14. Then, the sequence program and the prepared S-parameter are transmitted to the pair-loader transmitting and receiving control section 6 through the cable 4. If the data received by section 6 are the S-parameter, the pair-loader transmitting and receiving control section 6 transmits the received data to the parameter setting data area 8 through the data bus 14. If the data received by section 6 are the sequence program, the pair-loader transmitting and receiving control section 6 transmits the data to the sequence program area 11 through the data bus 15.
The parameter setting data area 8 stores the latching setting data from the S-parameter to the latching setting area 9, while the L-parameter is saved in the link setting area 10. The L-parameter is operative to effect transmission of the data to the data link control section 7 through the data bus 16A. The sequence control section 12 reads out the sequence program from the sequence program area 11 through the data bus 18, and reads out the S-parameter from the parameter setting data area 8 through the data bus 19, and executes the sequence program.
Furthermore, the data link control section 7 sets cyclic data generated due to cyclic communication with respect to other stations, to the 2-port RAM 13 through the data bus 16B, while the sequence control section 12 reads out cyclic data from the 2-port RAM 13 through the data bus 17, and uses the cyclic data as data for executing sequence computations.
In the above-described conventional network system, a loader 5 is connected, respectively, to every station. Each loader 5 executes the setting of the S-parameter for every other station. For this reason, if there are 64 stations, the loader 5 is required to set the S-parameter for 64 stations. Further, since the parent station 1 does not grasp the S-parameter for various child stations 2, it is impossible to grasp information such as latching setting or the like for every stations, and the like.
Next, latching/unlatching in the case where the data of the parent station 1 and of the child stations 2 are inputted and outputted at a remote location will be described. FIG. 16 shows an H/W switch 82 for setting latching/unlatching on a board or disc surface of the station. FIG. 17 is a flow chart showing the initial treatment or processing regarding the latching/unlatching at start-up of the stations. Information of the H/W switch 82 is read out (S83). It is judged in which one of the latching/unlatching positions (ON/OFF) the H/W switch 82 is set (S84). Here, if the H/W switch 82 is "ON", a program proceeds to latching processing (S85), while, if the H/W switch 82 is "OFF", the program proceeds to unlatching processing (S86).
In the conventional arrangement of a station data linked within the network, the child station 2 will be paralleled off from the data link when there is the generation of an abnormality, such as resetting or turning-off of an electric power source. In stations other than the paralleled-off station, the data existing immediately before paralleling-off of the paralleled-off child station 2 are latched.
Further, in the conventional example, in a station in which battery back-up is not provided the existence of an abnormality, resetting or turning-off of an electric power source occurs in the data link so that, in case where the child stations 2 are paralleled-off from the data link, inputting and outputting data cannot be latched. This will be described using the flow chart in FIG. 18.
In FIG. 18, the initial processing of a microcomputer within the data link control section 7, in order to establish a data link, is executed (S87). Then, the L-parameter is received from the parent station 1 (S88). It is checked whether or not the L-parameter is properly allotted with reference to a link device allotted to a local station (S89). Then, it is judged whether the checking results are OK or NG (S90). If the checking results are NG, error processing is executed (S92), and the program proceeds to step S88 in order to again receive the. L-parameter from the parent station 1. On the contrary, if the checking results are OK, a data link is established (S91).
In addition to the above, as reference technical literatures relating to the present invention, there are "BUS-TYPE INFORMATION TRANSMITTING APPARATUS" disclosed in. Japanese Patent Laid-Open No. HEI 2-301339, "FAULT INFORMATION COLLECTING SYSTEM" disclosed in Japanese Patent Laid-Open No. HEI 1-231594, "INHERENT OR INTRINSIC INFORMATION SETTING METHOD OF DISTRIBUTED-TYPE NETWORK" disclosed in Japanese Patent Laid-Open No. SHO 63-7051, and "REMOTE SUPERVISORY APPARATUS" disclosed in Japanese Utility Model Lid-Open No. SHO 59-91060.
According to the conventional network system described above:
(1) Since latching setting can be executed only individually, the latching setting must be executed for the number of stations connected to the network, and the operator must be moved around a factory in order to execute the latching setting.
(2) Since latching setting operations of the child stations cannot be monitored or supervised by the parent station, the latching setting operation for the entire network system cannot be centrally controlled or managed by the parent station.
(3) In case where a latching setting is made in the child stations by a H/W switch, it is impossible to alter or modify the contents of the latching setting.
Thus, there is a problem that, from the above-described factors or causes (1).about.(3), in the conventional network system, operational efficiency is low.
Further, according to the conventional network system:
(1) In a case where a problem station connected to the network is paralleled off from the data link due to the presence of abnormalities and the like, it is impossible to choose or select in other stations the latching/unlatching of the data just or immediately before paralleling-off of the problem station.
(2) It is impossible to select latching/unlatching of the data in a case where the local stations are paralleled off from the data link in a remote I/O station.
From the above-described factors (1) and (2), there is a problem in safety and reliability in the conventional network system.